In recent years, encapsulating semiconductor devices with an epoxy resin composition is mainly conducted due to an excellent balance among productivity, cost, reliability, and the like. Along with miniaturization of semiconductor devices, epoxy resin compositions for encapsulating the semiconductor devices are required to have lower viscosity, higher strength, and lower water absorption than ever before. For this reason, a recent tendency of epoxy resin compositions is to use a resin with lower viscosity and a larger amount of inorganic fillers. From the viewpoint of reducing environmental stress, a lead-free solder with a higher melting point is widely used for mounting semiconductor devices. A problem of this type of solder is the requirement for a mounting temperature that is about 20° C. higher than that required for conventional solders, which results in unduly impaired reliability of semiconductor devices after mounting. For these reasons, promoting reliability of semiconductor devices by improving epoxy resin compositions is urgently desired. Since improvement of adhesiveness of a resin with materials forming semiconductor devices, along with improvement of the strength and reduction of water absorptivity of cured epoxy resin compositions, is an important factor for improving reliability of semiconductor devices, a technique of increasing adhesion and high filler loading has been employed.
On the other hand, with regard to the manufacturing system for semiconductor devices, since the number of packages fabricated in one shot has increased and the shot time for fabricating semiconductor devices has been reduced to decrease the production cost, an epoxy resin composition that can be quickly cured and easily released from a mold is desired.
Although a number of researches have been undertaken to satisfy these requirements and their results have been reported in a number of publications, the methods developed heretofore solve only one or two problems among the many outstanding problems. A process that can satisfy all of these requirements and can be applicable on an across-the-board basis has not yet been developed.
Japanese Patent Application Laid-open No. 2002-220511 discloses a method for increasing adhesiveness of an epoxy resin composition, which comprises an epoxy resin, a phenol curing agent, a curing accelerator, and an inorganic filler, with construction materials of semiconductor devices by adding an adhesion promoter such as a coupling agent. Since the addition of an adhesion promoter impairs releasability, the productivity of the resulting resin composition is not satisfactory. In the case of a technique of adding a curing accelerator with an objective of reducing the molding cycle, the resin composition has impaired flowability, making it difficult to increase the amount of inorganic filler. The resulting resin composition has only unsatisfactory reliability. If a large amount of releasing agent is added to improve mold releasability, not only adhesiveness of the lead frame for mounting the semiconductor device with the cured product of the epoxy resin composition is impaired, but also a considerable amount of the releasing agent oozes from the mold surface and stains the surfaces of the mold and semiconductor packages.
Japanese Patent Application Laid-open No. 2002-80695 discloses an epoxy resin composition for encapsulating semiconductors, in which glycerol tri-fatty acid ester produced by a dehydration condensation reaction of glycerol and a saturated fatty acid with a carbon atom content of 24-36 is added to an epoxy resin composition comprising an epoxy resin, a phenol curing agent, a curing accelerator, and an inorganic filler to promote mold releasability. The epoxy resin composition for encapsulating semiconductors not only exhibits excellent mold releasability, but also can reduce stains on the surfaces of the mold and semiconductor packages. However, the effect of reducing stains on the surfaces of the mold and semiconductor packages of the epoxy resin composition is still insufficient.
In view of this situation, development of a technique ensuring high productivity and high reliability of semiconductor devices is strongly desired.